Coating composition and method for producing precoated steel sheets

- NKK Corporation

This invention relates to a coating composition for precoated steel sheets which are required to have high hardness, high workability and high distinctness of image, and to a method for producing a precoated steel sheet having a coating film of the composition. The composition is prepared by adding a compound of any of the following (a) to (c) to a coating composition consisting essentially of a polyol and containing, as the curing agent, an isocyanate compound or an amino resin, and the coating film of the composition has both high-level workability and high-level hardness.(a) Polyester compounds comprising main repeating units of a general formula (1): ##STR1## wherein n is an integer; and R is an alkylene group having 10 or less carbon atoms, or a 1,4-cyclohexylene-dimethylene group, or a neopentylene group, or a polyoxyalkylene group.(b) Polyester compounds comprising main repeating units of a general formula (2): ##STR2## wherein n is an integer of 10 or less; and R is an alkylene group having 10 or less carbon atoms, or a 1,4-cyclohexylene-dimethylene group, or a neopentylene group.(c) Compounds having the structure of a general formula (3):HO--(CH.sub.2).sub.n --O--R--O--(CH.sub.2).sub.n --OH (3)wherein n is an integer of from 2 to 10; and R is ##STR3##

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Claims

1. A coating composition for precoated steel sheets, which consists essentially of:

i) from 1 to 15% by weight of a polyester compound comprising main repeating units of a general formula: ##STR15## wherein n represents an integer; and R represents an alkylene group having 10 or less carbon atoms, or a 1,4-cyclohexylene-dimethylene group, or a neopentylene group, or a polyoxyalkylene group;
ii) a polyol; and
iii) a curing agent.

2. The coating composition for precoated steel sheets as claimed in claim 1, wherein R in the general formula representing the polyester compound in i) is a 1,4-cyclohexylene-dimethylene group, or a neopentylene group, or a polyoxyalkylene group.

3. The coating composition for precoated steel sheets as claimed in claim 2, wherein R in the general formula representing the polyester compound in i) is a polyoxyalkylene group.

4. The coating composition for precoated steel sheets as claimed in claim 3, wherein the polyester compound has a reduced viscosity of 0.20 dl/g or less.

5. The coating composition for precoated steel sheets as claimed in claim 1, 2, 3 or 4, wherein the polyol in ii) comprises a polyester polyol except the polyester compound in i), and/or an acrylic polyol.

6. The coating composition for precoated steel sheets as claimed in claim 5, wherein the polyester polyol is a compound having at least two hydroxyl groups in one molecule and having a number average molecular weight of from 1000 to 50000.

7. The coating composition for precoated steel sheets as claimed in claim 5, wherein the acrylic polyol is a compound having at least two hydroxyl groups in one molecule and having a number average molecular weight of from 500 to 50000.

8. The coating composition for precoated steel sheets as claimed in claims 1, 2, 3 or 4, wherein the curing agent in iii) comprises an isocyanate compound and/or an amino resin.

9. The coating composition for precoated steel sheets as claimed in claim 8, wherein the isocyanate compound is a blocked isocyanate compound.

10. The coating composition for precoated steel sheets as claimed in claim 9, wherein the isocyanate compound that constitutes the blocked isocyanate compound is one selected from the group consisting of hexamethylene diisocyanate or its derivatives, tolylene diisocyanate or its derivatives, 4,4'-diphenylmethane diisocyanate or its derivatives, xylylene diisocyanate or its derivatives, isophorone diisocyanate or its derivatives, trimethylhexamethylene diisocyanate or its derivatives, hydrogenated tolylene diisocyanate or its derivatives, hydrogenated 4,4'-diphenylmethane diisocyanate or its derivatives, and hydrogenated xylylene diisocyanate or its derivatives.

11. The coating composition for precoated steel sheets as claimed in claim 8, which comprises an isocyanate compound as the curing agent and in which the ratio by mol of the isocyanato groups in the isocyanate compound to the hydroxyl groups in the polyester compound in i) and the polyol in ii), NCO/OH is from 0.8 to 1.2.

12. The coating composition for precoated steel sheets as claimed in claim 8, which comprises an amino resin as the curing agent and in which the ratio of the combination of the polyester compound in i) and the polyol in ii) to the amino resin, (polyester compound+polyol)/amino resin, is from 95/5 to 65/35, in terms of the ratio by weight of the solid contents of these.

13. The coating composition for precoated steel sheets as claimed in claim 1, 2, 3, or 4, wherein the polyol in ii) comprises a polyester polyol except the polyester compound in i), and/or an acrylic polyol, and the polyester polyol is a compound having at least two hydroxyl groups in one molecule and having a number average molecular weight of from 1000 to 50000.

14. The coating composition for precoated steel sheets as claimed in claim 1, 2, 3, or 4, wherein the polyol in ii) comprises a polyester polyol except the polyester compound in i), and/or an acrylic polyol, and the acrylic polyol is a compound having at least two hydroxyl groups in one molecule and having a number average molecular weight of from 500 to 50000.

15. The coating composition for precoated steel sheets as claimed in claim 1, 2, 3, or 4, wherein the polyol in ii) comprises a polyester polyol except the polyester compound in i), and/or an acrylic polyol, and the polyester polyol is a compound having at least two hydroxyl groups in one molecule and having a number average molecular weight of from 1000 to 50000, and the acrylic polyol is a compound having at least two hydroxyl groups in one molecule and having a number average molecular weight of from 500 to 50000.

16. The coating composition for precoated steel sheets as claimed in claim 1, 2, 3, or 4, wherein the polyol in ii) comprises a polyester polyol except the polyester compound in i), and/or an acrylic polyol, the polyester polyol is a compound having at least two hydroxyl groups in one molecule and having a number average molecular weight of from 1000 to 50000, and the curing agent in iii) comprises an isocyanate compound and/or an amino resin.

17. The coating composition for precoated steel sheets as claimed in claim 1, 2, 3, or 4, wherein the polyol in ii) comprises a polyester polyol except the polyester compound in i), and/or an acrylic polyol, the acrylic polyol is a compound having at least two hydroxyl groups in one molecule and having a number average molecular weight of from 500 to 50000, and the curing agent in iii) comprises an isocyanate compound and/or an amino resin.

18. The coating composition for precoated steel sheets as claimed in claim 1, 2, 3, or 4, wherein the polyol in ii) comprises a polyester polyol except the polyester compound in i), and/or an acrylic polyol, the polyester polyol is a compound having at least two hydroxyl groups in one molecule and having a number average molecular weight of from 1000 to 50000, and the acrylic polyol is a compound having at least two hydroxyl groups in one molecule and having a number average molecular weight of from 500 to 50000, and the curing agent in iii) comprises an isocyanate compound and/or an amino resin.

19. The coating composition for precoated steel sheets as claimed in claim 1, 2, 3, or 4, wherein the polyol in ii) comprises a polyester polyol except the polyester compound in i), and/or an acrylic polyol, the polyester polyol is a compound having at least two hydroxyl groups in one molecule and having a number average molecular weight of from 1000 to 50000, and the curing agent in iii) is a blocked isocyanate compound.

20. The coating composition for precoated steel sheets as claimed in claim 1, 2, 3, or 4, wherein the polyol in ii) comprises a polyester polyol except the polyester compound in i), and/or an acrylic polyol, the acrylic polyol is a compound having at least two hydroxyl groups in one molecule and having a number average molecular weight of from 500 to 50000, and the curing agent in iii) is a blocked isocyanate compound.

21. The coating composition for precoated steel sheets as claimed in claim 1, 2, 3, or 4, wherein the polyol in ii) comprises a polyester polyol except the polyester compound in i), and/or an acrylic polyol, the polyester polyol is a compound having at least two hydroxyl groups in one molecule and having a number average molecular weight of from 1000 to 50000, the acrylic polyol is a compound having at least two hydroxyl groups in one molecule and having a number average molecular weight of from 500 to 50000 and the curing agent in iii) is a blocked isocyanate compound.

22. The coating composition for precoated steel sheets as claimed in claim 19, wherein the isocyanate compound that constitutes the blocked isocyanate compound is one selected from the group consisting of hexamethylene diisocyanate or its derivatives, tolylene diisocyanate or its derivatives, 4,4'-diphenylmethane diisocyanate or its derivatives, xylylene diisocyanate or its derivatives, isophorone diisocyanate or its derivatives, trimethylhexamethylene diisocyanate or its derivatives, hydrogenated tolylene diisocyanate or its derivatives, hydrogenated 4,4'-diphenylmethane diisocyanate or its derivatives, and hydrogenated xylylene diisocyanate or its derivatives.

23. The coating composition for precoated steel sheets as claimed in claim 20, wherein the isocyanate compound that constitutes the blocked isocyanate compound is one selected from the group consisting of hexamethylene diisocyanate or its derivatives, tolylene diisocyanate or its derivatives, 4,4'-diphenylmethane diisocyanate or its derivatives, xylylene diisocyanate or its derivatives, isophorone diisocyanate or its derivatives, trimethylhexamethylene diisocyanate or its derivatives, hydrogenated tolylene diisocyanate or its derivatives, hydrogenated 4,4'-diphenylmethane diisocyanate or its derivatives, and hydrogenated xylylene diisocyanate or its derivatives.

24. The coating composition for precoated steel sheets as claimed in claim 21, wherein the isocyanate compound that constitutes the blocked isocyanate compound is one selected from the group consisting of hexamethylene diisocyanate or its derivatives, tolylene diisocyanate or its derivatives, 4,4'-diphenylmethane diisocyanate or its derivatives, xylylene diisocyanate or its derivatives, isophorone diisocyanate or its derivatives, trimethylhexamethylene diisocyanate or its derivatives, hydrogenated tolylene diisocyanate or its derivatives, hydrogenated 4,4'-diphenylmethane diisocyanate or its derivatives, and hydrogenated xylylene diisocyanate or its derivatives.

25. The coating composition for precoated steel sheets as claimed in claim 16, which comprises an isocyanate compound as the curing agent and in which the ratio by mol of the isocyanato groups in the isocyanate compound to the hydroxyl groups in the polyester compound in i) and the polyol in ii), NCO/OH, is from 0.8 to 1.2.

26. The coating composition for precoated steel sheets as claimed in claim 17, which comprises an isocyanate compound as the curing agent and in which the ratio by mol of the isocyanato groups in the isocyanate compound to the hydroxyl groups in the polyester compound in i) and the polyol in ii), NCO/OH, is from 0.8 to 1.2.

27. The coating composition for precoated steel sheets as claimed in claim 18, which comprises an isocyanate compound as the curing agent and in which the ratio by mol of the isocyanato groups in the isocyanate compound to the hydroxyl groups in the polyester compound in i) and the polyol in ii), NCO/OH, is from 0.8 to 1.2.

28. The coating composition for precoated steel sheets as claimed in claim 19, which comprises an isocyanate compound as the curing agent and in which the ratio by mol of the isocyanato groups in the isocyanate compound to the hydroxyl groups in the polyester compound in i) and the polyol in ii), NCO/OH, is from 0.8 to 1.2.

29. The coating composition for precoated steel sheets as claimed in claim 20, which comprises an isocyanate compound as the curing agent and in which the ratio by mol of the isocyanato groups in the isocyanate compound to the hydroxyl groups in the polyester compound in i) and the polyol in ii), NCO/OH, is from 0.8 to 1.2.

30. The coating composition for precoated steel sheets as claimed in claim 21, which comprises an isocyanate compound as the curing agent and in which the ratio by mol of the isocyanato groups in the isocyanate compound to the hydroxyl groups in the polyester compound in i) and the polyol in ii), NCO/OH, is from 0.8 to 1.2.

31. The coating composition for precoated steel sheets as claimed in claim 22, wherein the ratio by mol of the isocyanato groups in the isocyanate compound to the hydroxyl groups in the polyester compound in i) and the polyol in ii), NCO/OH, is from 0.8 to 1.2.

32. The coating composition for precoated steel sheets as claimed in claim 16, which comprises an amino resin as the curing agent and in which the ratio of the combination of the polyester compound in i) and the polyol in ii) to the amino resin, (polyester compound+polyol)/amino resin, is from 95/5 to 65/35, in terms of the ratio by weight of the solid contents of these.

33. The coating composition for precoated steel sheets as claimed in claim 17, which comprises an amino resin as the curing agent and in which the ratio of the combination of the polyester compound in i) and the polyol in ii) to the amino resin, (polyester compound+polyol)/amino resin, is from 95/5 to 65/35, in terms of the ratio by weight of the solid contents of these.

34. The coating composition for precoated steel sheets as claimed in claim 18, which comprises an amino resin as the curing agent and in which the ratio of the combination of the polyester compound in i) and the polyol in ii) to the amino resin, (polyester compound+polyol)/amino resin, is from 95/5 to 65/35, in terms of the ratio by weight of the solid contents of these.

35. A method for producing a precoated steel sheet, which comprises applying a coating composition as claimed in claim 1 onto a steel sheet or a plated steel sheet to form a coating film thereon.

36. The method for producing a precoated steel sheet as claimed in claim 35, wherein the steel sheet or the plated steel sheet onto which the coating composition is applied is surface-treated and/or undercoated with a primer.

37. A precoated steel sheet having a coating film formed from a coating composition as claimed in claim 1.

38. The precoated steel sheet as claimed in claim 37, wherein the substrate is a steel sheet or a plated steel sheet, and the steel sheet or the plated steel sheet is surface-treated and/or undercoated with a primer.

39. The coating composition for precoated steel sheets as claimed in claim 23, wherein the ratio by mol of the isocyanato groups in the isocyanate compound to the hydroxyl groups in the polyester compound in i) and the polyol in ii), NCO/OH, is from 0.8 to 1.2.

40. The coating composition for precoated steel sheets as claimed in claim 24, wherein the ratio by mol of the isocyanato groups in the isocyanate compound to the hydroxyl groups in the polyester compound in i) and the polyol in ii), NCO/OH, is from 0.8 to 1.2.

Referenced Cited
U.S. Patent Documents
5418309 May 23, 1995 Tanabe et al.
5543475 August 6, 1996 Jones et al.
Foreign Patent Documents
56-18032 April 1981 JPX
59-11370 July 1984 JPX
62-195057 August 1987 JPX
62-236817 October 1987 JPX
63-108081 May 1988 JPX
90012250 March 1990 JPX
2-209979 August 1990 JPX
3-500544 February 1991 JPX
6-506243 July 1994 JPX
6-234752 August 1994 JPX
Patent History
Patent number: 5817731
Type: Grant
Filed: Sep 3, 1996
Date of Patent: Oct 6, 1998
Assignee: NKK Corporation (Tokyo)
Inventors: Kenji Yoshida (Tokyo), Takashi Anyashiki (Tokyo), Kazumi Itou (Tokyo), Shouichi Oosuka (Tokyo)
Primary Examiner: Rachel Gorr
Law Firm: Nields, Lemack & Dingman
Application Number: 8/707,249
Classifications
Current U.S. Class: From At Least One Blocked -n=c=x Group (528/45); Reactant Contains At Least One Bridged- Or Fused-ring System (528/74); Metal Base (427/409); 428/4258; 428/4259
International Classification: C08G 1880;